Preterm delivery (PTD) is the principal underlying cause of infant mortality in the U.S. and contributes substantially to childhood handicap, particularly in high risk groups such as African Americans and poor women. Little progress has been made in prevention, and preterm delivery rates (which are already double those of many European nations) continue to rise steadily in the U.S. Preliminary work confirms that elevation in serum alpha fetoprotein (MSAFP, a routinely obtained screening test for fetal defect) is the best early biomarker of risk of preterm delivery in both white and African American women. But it is not understood how MSAFP and PTD are related, nor how the social context of poverty influences risk of either elevated MSAFP or PTD. The aims of this study are to establish the pathways through which risk of PTD is mediated and the role of MSAFP in these pathways. The investigators hypothesize that one major pathway to PTD is placental dysfunction, for which MSAFP is a biomarker. They will enroll 348 women with high and 1677 women with normal MSAFP levels at 15-20 weeks, stratified by race, and follow them until delivery in 14 hospitals in Michigan that are linked to the community campuses of the medical school. Through interviews, record reviews and assays of serum, plasma and vaginal flora, information will be obtained about the social environment, psychological factors, health behaviors, reproductive and health histories, and biomarkers of placental function and infection in study subjects. Stored serum will be available for future biomarker studies. Using the case-cohort design, women delivering prematurely, and a random sample of the remainder, will be studied more intensively, with a special focus on placental pathology and on biomarkers of vascular disease and infection. The investigators state that by integrating psychosocial, clinico-pathological and biomarker data, biologically coherent pathways to PTD (and the extent to which they are or are not mediated via elevated MSAFP) may be discerned, thus suggesting prevention strategies for the future.